Since then I've moved to Kubuntu (based on Ubuntu but with the KDE desktop), which worked well up to Kubuntu 15.04. Since then I have now upgraded to the latest version Kubuntu 15.10 which has now resulted in more problems due to the clickpad. I've created a workaround, although it's still not quite how I'd want it working.

I've referred to this as a clickpad, although it's also known as a soft touchpad. As you can see from the photo above instead of having separate buttons underneath the touchpad the touchpad is a single piece with a painted line indicating where the left and right buttons are. Instead of having multiple buttons it is down to the finger position whether it is taken as a left or right button press.
The problem is that when using one finger to press the button and a second as the drag (as you would on a normal touchpad), then the touchpad sees this as a mutli-touch gesture. In earlier versions of Ubuntu the clickpad behaviour could be changed by setting the detectable area for the touchpad, but this no longer appears to work in Ubuntu 15.10.

I haven't been able to get it working as I would like to, but I have managed to change the behaviour so that it is more usable.

The change I made was to disable the I2C driver and instead rely on the usb driver. This is done by editing /etc/modprobe.d/blacklist.conf

Add the entries:

blacklist i2c_hid
blacklist mac_hid

then update using:

sudo depmod -a
sudo update-initramfs -u

This does not completely fix the erratic behaviour, but the usb driver works slightly better.

To drag a window etc. then I first need to put my drag finger onto the touchpad and then whilst leaving my finger on the trackpad click the button on the button part of the trackpad with another finger.

Unfortunately there is no indication of a better fix on the Dell website. Although they do supply one laptop with Ubuntu pre-installed, they don't provide any support for the 7000 series and I don't know whether the Ubuntu laptop has the same clickpad. There is no mention of support for this on their website.

I've got the touchpad so that it is usable, but it's still not idea. Unless anyone has any other suggestions, I'll be avoiding buying a laptop with a similar touchpad until this is fixed in Ubuntu / Kubuntu.